This invention relates to an improved orifice unit assembly for use as a needle valve flow meter provided in a gas or liquid system.
Orifice valve assemblies are known which include a metalic orifice holder element, a synthetic resin material orifice unit fitting tightly within the holder element and having an end wall at one end thereof, and a metallic tapered or bevel-ended needle reciprocable through the orifice, whereby the tapered needle will regulate the amount of fluid flow through the orifice.
However, such known assemblies suffer from the disadvantages that variations in temperature cause the rate of expansion and contraction of the resin material orifice unit to be greater than that of the metallic holder unit and needle, and that such temperature variations result in variations in the viscous resistance of gas. Therefore, it is difficult to maintain a constant flow rate through the orifice.